AdWords and Time Delay

I have experienced this many times already, but I am not sure if there is some kind of rule or why it is happening. When I start a new [tag]Adwords[/tag] campaign it doesn´t seem to start (get impressions and clicks) immediately. Lately it has taken hours before my campaigns have been activated, at least this is what it seems. When I first started to use AdWords, I started to get impressions and clicks after a few minutes. Now I am not sure if I am doing something wrong or if they have put a delay on AdWords, because of a growing amount of users or some other reasons. I am so eager for my campaigns to start, I keep waiting and waiting ... and nothing happens. In the end, my campaigns starts, but I keep thinking that maybe the campaign and the keywords I have chosen are not that good, because nothing happens. [tag]Google[/tag] keeps telling me that I should be getting a good amoung of clicks a day, but when nothing happens for a few hours, I am starting to question the information from Google.